首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   32865篇
  免费   3975篇
  国内免费   1879篇
电工技术   6612篇
技术理论   2篇
综合类   1728篇
化学工业   5823篇
金属工艺   2060篇
机械仪表   1025篇
建筑科学   608篇
矿业工程   395篇
能源动力   5552篇
轻工业   945篇
水利工程   510篇
石油天然气   2262篇
武器工业   142篇
无线电   2369篇
一般工业技术   3091篇
冶金工业   1239篇
原子能技术   544篇
自动化技术   3812篇
  2024年   204篇
  2023年   1041篇
  2022年   1476篇
  2021年   1556篇
  2020年   1518篇
  2019年   1313篇
  2018年   1065篇
  2017年   1305篇
  2016年   1305篇
  2015年   1307篇
  2014年   2104篇
  2013年   2064篇
  2012年   2364篇
  2011年   2594篇
  2010年   1855篇
  2009年   1926篇
  2008年   1623篇
  2007年   1799篇
  2006年   1622篇
  2005年   1387篇
  2004年   1192篇
  2003年   959篇
  2002年   876篇
  2001年   770篇
  2000年   623篇
  1999年   473篇
  1998年   393篇
  1997年   323篇
  1996年   285篇
  1995年   261篇
  1994年   214篇
  1993年   169篇
  1992年   129篇
  1991年   110篇
  1990年   119篇
  1989年   73篇
  1988年   51篇
  1987年   38篇
  1986年   25篇
  1985年   43篇
  1984年   48篇
  1983年   26篇
  1982年   20篇
  1981年   10篇
  1980年   12篇
  1979年   10篇
  1978年   6篇
  1977年   6篇
  1974年   5篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 4 毫秒
61.
Thin-layer carbon supported Nafion-H catalysts were found to be active and highly selective (S>98%) for the partial oxidation of C1-C3 alkanes, in a three phase catalytic membrane reactor (3PCMR), under mild conditions and in the presence of H2O2. The influences of the catalyst teflon loading and H2O2 concentration on the reaction rate have been evaluated. A reaction pathway, based on the electrophilic hydroxylation of the C-H bond of alkanes with protonated hydrogen peroxide (H3O 2 + ), is discussed.  相似文献   
62.
本文简要介绍了国外在开发超酸性气体过程中遇到的材料选择、腐蚀监测、水化物堵塞、超酸性气的处理和加工等问题所采取的措施和办法。  相似文献   
63.
刘鹏 《山西电子技术》2004,(4):22-24,39
在光纤高速传输技术、光交换与智能光网等与宽带接入、多媒体、3G等网络应用技术的推动下,建设基于IPv6协议的IP基础电信网成为可能。现在IP网正在朝着有序的、可管理的、有QoS保障的、可以支持各类业务的综合业务基础网演进。电信网也正在从网络接入层上、从长途网络层面上、从本地网络层面上、从固定网向含3G在内的移动网络等方面向支持IP技术及其综合业务的方面全面推进。  相似文献   
64.
When a linear voltage ramp is applied to the gate of a MOS capacitor, a capacitancetime (C-t) transient is observed. The MOS capacitor is biased into strong inversion before applying the voltage ramp in order to eliminate surface generation. FromC-t transient curve obtained experimentally the minority carrier generation lifetime in semiconductor can be determined. The experimental results show that for the same sample the lifetimes extracted fromC-t curves under varying voltage sweep rates are close each other, and they are consistent with the lifetimes extracted by saturation capacitance method.  相似文献   
65.
过氧化氢爆炸事故浅析   总被引:6,自引:1,他引:5  
通过两起过氧化氢(双氧水)爆炸事故,分析了过氧化氢由于本身具有较大的潜能,很不稳定,当受热、泄漏、撞击、摩擦时,易分解放热产生高温,造成火灾爆炸事故,对火灾爆炸反应过程与爆炸机理进行了探讨。  相似文献   
66.
Lamellar zinc pigment reacts in aqueous alkaline media (e.g., water-borne paints) with the evolution of hydrogen. This corrosion reaction can be inhibited by 2-nitrophenol (2-NP), 2,4-dinitrophenol (2,4-DNP), 2-hydroxy-3,5-dinitro-benzoic acid (HDNBA) and 2-hydroxy-3-nitro-benzoic acid (2-H-3-NBA) which all have a nitro-group ortho to a hydroxy-group; this structural part of the inhibitors can be considered as a potential chelating group which may explain the corrosion inhibiting effect. As a rule, with triethylamine (TEA) as neutralizing agent corrosion inhibition is slightly better when compared to dimethylethanolamine (DMEA). With TEA there is complete corrosion inhibition with addition of 2,4-DNP at pH 8 and 10; with 2-H-3-NBA there is complete inhibition at pH 10.  相似文献   
67.
In this paper we derive kinetic parameters for the generation of gaseous hydrocarbons (C1‐5) and methane (C1) from closed‐system laboratory pyrolysis of selected samples of marine kerogen and oil from the SW Tarim Basin. The activation energy distributions for the generation of both C1‐5 (Ea = 59‐72kcal, A = 1.0×1014 s?1) and C1 (Ea = 61‐78kcal, A = 6.06×1014 s?1) hydrocarbons from the marine oil are narrower than those for the generation of these hydrocarbons from marine kerogen (Ea = 50‐74kcal, A = 1.0×1014 s?1 for C1‐5; and Ea = 48‐72kcal, A=3.9×1013 s?1 for C1, respectively). Using these kinetic parameters, both the yields and timings of C1‐5 and C1 hydrocarbons generated from Cambrian source rocks and from in‐reservoir cracking of oil in Ordovician strata were predicted for selected wells along a north‐south profile in the SW of the basin. Thermodynamic conditions for the cracking of oil and kerogen were modelled within the context of the geological framework. It is suggested that marine kerogen began to crack at temperatures of around 120°C (or 0.8 %Ro) and entered the gas window at 138°C (or 1.05 %Ro); whereas the marine oil began to crack at about 140 °C (or 1.1 %Ro) and entered the gas window at 158 °C (or 1.6%Ro). The main geological controls identified for gas accumulations in the Bachu Arch (Southwest Depression, SW Tarim Basin) include the remaining gas potential following Caledonian uplift; oil trapping and preservation in basal Ordovician strata; the extent of breaching of Ordovician reservoirs; and whether reservoir burial depths are sufficiently deep for oil cracking to have occurred. In the Maigaiti Slope and Southwest Depression, the timing of gas generation was later than that in the Bachu Arch, with much higher yields and generation rates, and hence better prospects for gas exploration. It appears from the gas generation kinetics that the primary source for the gases in the Hetianhe gasfield was the Southwest Depression.  相似文献   
68.
HIC是腐蚀试验中常用的检测方法,用来测评材料在含硫化氢环境中对氢离子敏感性大小.其包含两种不同的腐蚀介质,不同的腐蚀介质中酸碱度是不一样的,腐蚀介质的酸碱度对试验结果有较大的影响,为此,运用电离平衡理论,计算并分析两种不同腐蚀介质电离平衡前后的氢离子浓度变化,得出动态反应平衡时氢离子浓度的关系式,从而获得介质中精确的氢离子浓度,并对腐蚀介质中相关离子进行了探讨,为进一步探究相关环境中的腐蚀机理提供了依据.  相似文献   
69.
The development of renewable technologies in the last decade has been exceptional. In photovoltaic (PV) for example, efforts were not only limited to merely improving their efficiency but also to the reduction of the cost of cells and modules via volume production for commercial markets. There are many national schemes promoting the use of PV technology and regional targets for a share of renewable energy production. This paper attempts to relay to the reader a journey, based on experience, approaches for enhancing the prospect of utilising solar energy within the society we live in. The issue of expansion or enhancing the utilisation of solar energy can be undertaken by individuals, groups, institutions and governments. The aim of this paper is to provide some examples, which could serve as a framework in which action could be taken to promote solar technology.  相似文献   
70.
利用带镍加氢转化炉的气相色谱仪 ,在线分析变压吸附法制纯氢中的总碳。该法用变压吸附法制的纯氢作燃气 ,在检测器前端将氢气中的CO和CO2 转化为CH4,然后用氢火焰离子化检测器检测 ,直接以检测器的信号 (mV)进行定量。当氢气中总碳体积分数在 1 9~ 5 0 0 μl/L时 ,FID信号值与总碳体积分数有良好的线性关系。方法回收率为 99 90 %~ 10 1 9%,相对标准偏差 <1%。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号